1. Field of the Invention
The present invention relates to an electroluminescent device [also referred to as xe2x80x9cEL devicexe2x80x9d in the following], and in particular to an electroluminescent device with a flattened electroluminescent layer [also referred to as xe2x80x9cEL layerxe2x80x9d in the following].
2. Description of the Prior Art
FIG. 1 shows the basic structure of an organic EL device with a color filter. The organic EL device 50 includes a color filter 59, an anode electrode 57 made of ITO, an organic EL layer 56, and a cathode electrode 55, formed in this order on a glass substrate 53 serving as a supporting member. The organic EL layer 56 consists of a hole transport layer 56a and an emitter layer 56b. When a predetermined voltage is applied between the anode electrode 57 and the cathode electrode 55, the emitter layer 56b emits light, which is emitted through the color filter 59 and the glass substrate 53.
FIG. 2 shows a color organic EL device 60, whose anode electrodes and cathode electrodes are arranged in form of a matrix. The organic EL device 60 includes a plurality of color filters 64 extending in the row direction and lined up in the column direction 73, formed on a glass substrate 63 serving as the supporting member. A plurality of anode electrodes 67 made of ITO extending in the column direction and lined up in the row direction are formed on the color filters 64. An organic EL layer 66 extending over the entire substrate is formed on top of the anode electrodes 67. A plurality of cathode electrodes 65 extending in the row direction and lined up in the column direction are formed on top of the organic EL layer 66.
Selecting the anode electrodes 67 and cathode electrodes 65 to which a voltage is applied, the organic EL layer 66 emits light at the desired locations, which is transmitted through the color filter 64 and the glass substrate 63, and emitted in the arrow direction 75.
This organic EL device 60, however, has the following problems. In this organic EL device 60, the anode electrodes 67, the organic EL layer 66, and the cathode electrodes 65 are formed after forming the color filter 64, because the color filter 64, the anode electrodes 67, the organic EL layer 66, and the cathode electrodes 65 are formed in this order on the glass substrate 63. Consequently, the anode electrodes 67, the organic EL layer 66, and the cathode electrodes 65 have to be formed under conditions that do not destroy the color filter 64, which has already been formed. The forming conditions (such as material quality and temperatures) for those electrodes and for the organic EL layer 66 are limited to conditions that the color filter 64 can withstand. Also, because the anode electrodes 67, the organic EL layer 66, and the cathode electrodes 65 are formed on the color filter 64, the surface of the color filter 64 has to be smooth.
Moreover, the organic EL layer 66 is about 100 nm thick, whereas the thickness of the color filter 64 is about 1 to 3 xcexcm. When such a thin organic EL layer is formed on top of the color filter 64 with its sharp differences in level, there is the danger that the organic EL layer becomes thinner at corner portions of the level differences. Electric fields concentrate at the thin portions of the organic EL layer, which leads to light emission irregularities. The amount of light emitted from the organic EL layer is inversely proportional to the third power of its film thickness, so that slight variations of the film thickness have a large influence on the amount of emitted light.
With the foregoing drawbacks of the prior art in view, it is an object of the present invention to present an EL device with color filter, allowing the EL layer to be made flat.
An organic EL device of the present invention includes 1) a lower electrode formed in or on a substrate with a flat surface, 2) an organic EL layer formed on top of the lower electrode, 3) a transparent upper electrode formed on top of the organic EL layer, and 4) a color-converting layer arranged on top of the upper electrode.
The features of the present invention, other objects, uses and merits should become clearer from the following examples, with reference to the accompanying drawings.